A housing of electronic devices, such as mobile phones having electroacoustic transducers, e.g., a loudspeaker, a microphone, and a receiver; compact radios; transceivers; portable music players; laptop computers; headphones; earphones; outdoor microphones; and digital cameras, is provided with at least one sound hole for allowing a sound to pass from the inside to the outside, or from the outside to the inside, of the housing. A waterproof filter (or a waterproof film) is attached to the sound hole for the main purpose of preventing water from entering the inside of the electronic device.
As an example of such a waterproof film, Patent Document 1 discloses a mobile communication terminal in which electroacoustic transducers, such as a telephone receiver, a telephone transmitter, and a buzzer, are mounted to internal annular projections formed so as to surround small acoustic holes of a housing, the mobile communication terminal having a structure in which a piece of waterproof paper is provided between the small hole and the acoustic part; only the peripheral portion of the piece of waterproof paper is fixed between the internal annular projection and an annular interposed member; and each electroacoustic transducer is mounted to the annular interposed member so as to form a first front air chamber in the inside of the electroacoustic transducer, a second front air chamber between the acoustic part and the piece of waterproof paper, and a third front air chamber between the piece of waterproof paper and the housing.
As another example of such a waterproof film, Patent Document 2 discloses a structure in which a concave portion is provided on the end surface of a microphone accommodation member for accommodating a microphone main unit. A microphone attachment portion of a case is provided with an opening. A supporting frame is provided around the opening in a projecting manner, so as to allow the microphone accommodation member to be inserted and fixed therein. An annular projection is provided in the inside of the supporting frame and around the opening in a projecting manner, so as to fit the concave portion of the microphone accommodation member.
The waterproof film to be used for the acoustic applications as described above requires allowing a sound to pass therethrough with high efficiency, and therefore, it must be fixed while remaining the state capable of vibrating. That is, the fixation of the waterproof film may desirably be limited to the peripheral portion of the waterproof film as much as possible. As an example thereof, Patent Document 3 discloses a structure in which a protective membrane (or a waterproof film) is sandwiched between two adhesive support systems (e.g., double-sided pressure-sensitive adhesive tapes) each having an opening. With this structure, upstream sound pressure waves vibrate the protective membrane, and the solid borne energy (i.e., mechanical vibration) of the protective membrane, which has been generated by the vibration, is converted into downstream sound pressure waves, resulting in low acoustic loss/attenuation.
A waterproof film is attached to at least one sound hole in the housing of electronic devices such as mobile phones. Electronic devices such as mobile phones are increasingly reduced in size and thickness, and accordingly, the waterproof film is required to be reduced in size and to be improved in accuracy for its attachment position.
To improve the accuracy in the positioning of a waterproof film or an electroacoustic transducer, it is contemplated that a stepped portion is formed in the housing of electronic devices so as to guide the waterproof film and the electroacoustic transducer (e.g., Patent Document 4). In this connection, such a stepped portion does not necessarily completely fit the waterproof film, and may be formed with some allowance as shown in FIG. 4 of Patent Document 4. In such a case, the stepped portion may not necessarily contribute directly to the positioning of the waterproof film, but is useful as a marker indicating the attachment position of the waterproof film.